Automatic defrosting control mechanism for heat pumps and the like



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AUTOMATIC DEF'ROSTING CONTROL MECHANISM FOR HEAT PUMPS AND THE LIKEFiled Dec; 11, 1963 4 Sheets-Sheet l INVENTORS v JOHN LIEBERMANN Mg. g

y ROBERT E BROOKS ATTO E A M; W; W 1%4 J4 LJEEEERMANN ETAL 3&20386AUTOMATIC DEE HOSTING CONTROL MECHANISM FOR HEAT PUMPS AND THE LIKE]Filed Dec. 11, 1963 4 Sheets-Sheet 2 980 med mam an: a:

4w 1 INVENTORS JOHN LiEBE-IRMANN a. a. BROOKS BY "7M (6 W y $195? JMEEERMANN ETAL ifi mm fifi AUTOMATlC DEFROSTING CONTROL MEEHAN Iv SM FORHEAT PUMPS ANT) THFI LT K 51 Filed D80. 11, 1965 4 SI'leets-Sheet 5 9 aiila IN VEN TORS JOHN LIEEIERMANN ROBERT E. BROOKS r a a y y $69?LEEBERMANN FETAL. 3,5203% AUTOMATlC DEFROSTING CONTROL MBCI'IANISM FORHEAT P UMF 5 AND TH 11 L1 K i Filed Dec. 11, 1965 4 Sheets-$heet 4 JOHNLEEBERMANN FZQBEZRT E. BROOKS United States Patent 3,320,386 AUTOMATICDEFROSTHNG CONTROL MEQHA- NISM FOR HEAT PUMPS AND THE LIKE JohnLiebermann, Columbus, and Robert E. Brooks,

Worthington, Ohio, assignors to Ranco Incorporated,

Columbus, Ohio, a corporation of Ohio Filed Dec. 11, 1963, Ser. No.329,816 Claims. (Cl. ZOO-136.3)

This invention relates to deice or defrosting controls for automaticallyremoving ice from evaporator coils of heat pumps of thecompressor-condenser-expander type refrigerating systems andparticularly of such heat pump systems when they are operated in theheating phase. As is well known in the art, when outdoor temperaturesare in the zone of about 50 F. and below, there is a tendency for ice toaccumulate on the outdoor coil or evaporator of heat pump systems of thetype mentioned when the system is on the heating cycle with an attendantreduction in heat exchange efficiency thereof. Numerous arrangementshave been proposed heretofore for effecting temporary reversal of thephase of operation of the system through solenoid valve means, etc., sothat the iced coil acts temporarily as a condenser, and the heattherefrom quickly melts the ice. However, no completely satisfactorysystem has been provided for automatically controlling the initiationand termination of this deicing cycle.

It is a principal object of this invention to provide a novel time andtemperature responsive switch or device control which is operative toperiodically establish capability of initiating a deicing cycle for anevaporator subject to the presence of a predetermined temperature at theevaporator sufficiently low to cause accumulation of ice on theevaporator, and which control terminates the deicing cycle uponattainment of a second higher temperature at the evaporator indicativeof the removal of the ice therefrom.

Another object of this invention is the provision of a deice control forrefrigeration systems and comprising an electric switch having anactuator member movable between first and second operative positions forrespec tively initiating and terminating deice cycles, the actuatormember being held between its operative positions during normaloperation of the system and urged toward its deice initiating positionby thermally responsive means in response to a predetermined lowtemperature at the evaporator, and timer operated means for blockingmovement of the actuator member to its deice cycle initiating positionexcept at predetermined intervals, whereby deice cycles are initiated bythe simultaneous occurrence of the low temperature and the passage of atimed interval.

Yet another object of this invention is the provision of a deice controlof the foregoing character wherein the thermally responsive meanscomprises a thermally expansible power element working against a primaryload means for determining the predetermined low temperature at whichthe actuator member is moved to its deice cycle initiating position, andmeansfor subjecting the expansible power element to an means forsubjecting the expansible power element to an additional or secondaryload upon temperature increases above normal operating temperature atthe evaporator, whereby the actuator member is moved by the thermallyresponsive means to its deice cycle terminating position only upon theattainment of a predetermined high temperature sufficient to melt theice at the evaporator.

Still another object of this invention is the provision of an improvedtime and temperature responsive deice control wherein the timer operatedblocking means may be adjusted to select the timed intervals at whichthe switch actuator member will be movable to its deice cycle initiatingposition if icing temperatures are present at the evaporator. In apreferred embodiment, the timer operated blocking means comprises anovel cam construction including a cam rotated at a predetermined rateand having a plurality of recesses in the periphery thereof forcooperation with cam follower means to determine the passage of timeintervals, and selectively positionable mask means for alternativelymasking or revealing one or more of said recesses to the cam followermeans so as to vary the time intervals, the mask being clutched in itsselected positions for rotation with the cam.

As another object this invention aims to provide a deice control whichis fail safe with regard to the thermally responsive portion thereof sothat in the unlikely event of failure of the thermal power element, suchas by loss of expansible fluid charge from a bellows or the like, thecontrol device will be conditioned to both initiate and terminate thedeice cycles on a purely time basis.

The invention may be further described as residing in certain novelconstructions and arrangements of parts by which the foregoing objectsand advantages, as well as others, are achieved, as will become apparentfrom the following detailed description of a presently preferred form ofdeicer control embodying the features of this invention.

In the accompanying sheets of drawings, forming a part of thisspecification FIG. 1 is a schematic illustration of a reversible heatpump system of the compressor-condenser-evaporator type including adeice control device embodying this invention; 7

FIG. 2 is an enlarged elevational view of the deice control device ofFIG. 1, with a fragmentary showing of the evaporator coil;

FIG. 3 is a bottom view of the deice control device of FIG. 2, viewedalong line 33 thereof;

FIG. 4 is an enlarged sectional view of the control device takensubstantially along line 4--4 of FIG. 3;

FIGS. 5 and 6 are views similar to FIG. 4 but showing some parts indifferent operating positions, and with some parts broken away forclarity;

FIG. 7 is a fragmentary sectional view taken along line 77 of FIG. 4;

FIG. 8 is a sectional view taken substantially along line 8-8 of FIG. 4;

FIG. 9 is an enlarged fragmentary view of a portion of the device viewedsubstantially along line 99 of FIG. 3; and

FIG. 10 is a still larger fragmentary view of the subject matter of FIG.9 with parts in section.

Referring to FIG. 1 of the drawings, there is illustrated therein areversible heat pump system of the type advantageously employing a deicecontrol device embodying this invention. The heat pump system comprisesa compressor-condenser-evaporator circuit including a motorcompressor10, a solenoid operated reversing valve 12, an indoor heat exchanger 18,an outdoor heat exchanger 19, and a capillary 20 providing flowrestriction between the heat exchangers. The heat exchangers 18 and 19are of conventional construction comprising coils of tubing 18a and 19awhich may be provided with fins, air conducting shrouds, and the like.

The motor-compressor 10 is connected by electrical conductors 21, 22,and a suitable thermostatic switch 23 to power lines L1 and L2. Thethemostatic switch 23 may be conveniently located in the space to betempered by the indoor heat exchanger 18, and cyclically energizes anddenergizes the motor-compressor as necessary to maintain a predeterminedtemperature level in the tempered space. The reversing valve 12comprises a solenoid 12a which is connected to power lines L1 and L2 bysuitable conductors 24, 25, and a deice control 26 embodying thisinvention and described in detail hereinafter.

The reversing valve 12 is actuable by energizing or deenergizing thesolenoid 12a thereof to condition the system to provide cooling orheating respectively of the space to be tempered by the indoor heatexchanger 18. Thus, when the space is to be heated, the indoor heatexchanger 18 serves as the condenser while the outdoor heat exchanger 19serves as the evaporator. In that phase of operation, refrigerant flowmay be traced from the discharge side of a motor-compressor 10 throughtube 28, reversing valve 12, tube 29, indoor heat exchanger 18,capillary 20, the outdoor heat exchanger 19 acting as the evaporator,tube 31, the reversing valve 12., and tube 32 to the intake side of themotor-compressor. Hot compressed gas from the motor compressor 10 iscondensed in the heat exchanger 18, thereby giving up heat to the spaceto be tempered. The condensed refrigerant then passes through thecapillary 20 for expansion in the heat exchanger 19 wherein therefrigerant takes on heat from air circulated over the tubing 19athereof. During such operation the coils of tubing 19a of the outdoorheat exchanger are cooled considerably, often to temperatures below thefreezing point of water. At times, such as during early morning hourswhen humidity is relatively high, there is a tendency for frost tocollect on the coils 19a, which frost insulates the coils and reducesthe heat exchange efficiency thereof.

The frost may be effectively removed by energizing the solenoid 12a tocause the valve 12 to reverse the flow of refrigerant to the heatexchangers 18 and 19 and thereby conditioning the system to effect atemporary heating of the outdoor heat exchanger 19 by hot compressedrefrigerant gas coming directly from the compressor 10. To this end, thedeice control device 26, embodying this invention, is operative toenergize the reversing valve solenoid 12a to effect heating of the heatexchanger 19 at timed intervals if the evaporator coils 19a are at orbelow freezing temperature as sensed by a hub 36 forming part of thecontrol 30 and connected therewith by a capillary tube 37, all as willbe described more fully hereinafter.

Referring now to the remainder of the drawings, the deice control device26 includes a generally rectangular sheet metal frame 41 having whatwill be referred to as side walls 41a and 41b, end walls 41c and 41d,and a top wall 41e, although it will be understood that the controldevice does not require any particular orientation in use. Mounted onthe frame 41 between the side walls 41a and 41b thereof, is provided anelectrical, snap acting switch 42 which includes an insulating baseportion 43 conveniently secured as by lugs 43a protruding from the baseportion into engagement with corresponding openings in the side walls41a and 41b. The switch 42, which in this example is a single poledouble throw switch, comprises terminals 44, 45 and 46, the terminals 45and 46 of which form part of a control circuit for the reversing valvesolenoid 12a.

Referring to FIGS. 4 and 7, the inner end of the terminal member 45 isformed into a conductor bar 47 overlying the insulating base portion 43and having a threaded opening in which is received a screw 48 carrying anormally stationary but adjustable contact 49. A movable double contact50 is carried on one end of a flexible switch arm 51 for snap actingmovement between stationary contact 49 and another stationary contact 52connected to the inner end of terminal 44 which is in the form of abridge 44a. The other end of the switch arm 51 is secured to the innerend 46a of terminal 46, and the arm is moved with a snap action bytoggle means operated by movement of a pivoted actuator arm 55. Theactuator arm 55 has laterally spaced bearing portions 56 pivoted onknife edged projections 57 on the inner end 46a of terminal 46 andcomprises a downturned hook 55a on its free end. A toggle spring 58extends between the hook 55a and a U-shaped toggle bar 59 disposed in acentral opening of the switch arm 51 and having pivotal engagement withthat arm near the free end thereof. The actuator arm 55 is biased in aclockwise direction about projections 57 under the influence of spring58, toward a position wherein the movable contact '50 is toggled intoengagement with the stationary contact 49, as shown in FIG. 5, tocomplete a circuit between terminals 45 and 46 for initiating adefrosting cycle. When the actuator arm 55 is rotated in acounterclockwise direction about projections 57, by means describedhereinafter, the toggle mechanism snaps the contact from the stationarycontact 49 to the stationary contact 52, as shown in FIG. 6, tointerrupt or terminate a defrosting cycle.

For reasons which will become apparent as the description proceeds,switch 42 is characterized by a substantial differential between thepositions of the actuator arm wherein the contact 50 is toggled betweenthe stationary contacts. Other well known forms of switch having anappreciable differential between the operative positions of an actuatorarm may be used in the practice of the invention, the switch 42 beingdescribed as a preferred example.

Movement of the actuator arm 55 to produce actuation of the switch 42 iseffected in part in response to predetermined temperature conditions ofthe evaporator as represented by temperature responsive means, and inpart in response to the passage of time as represented by a timing meansdescribed later herein. The temperature responsive means includes atemperature sensing element such as the bulb 36 which is disposedadjacent the outdoor coil 19a of a heat pump apparatus so that it sensesthe temperature of the air leaving the outdoor coil. The temperaturesensing bulb 36 is connected by a suitable capillary tube 37 to the base73 of an expansible power element or bellows 74. The base 73 of bellows74 is mounted on a cup member '75 having a flange 75a secured by screws76 to the end wall 410 of frame 41, with the bellows projecting througha window therein. The bellows 74 include an axially movable bellows post76 for transmitting motion to a bellows lever 80, presently described.The bulb 36, capillary tube 37, and bellows 74 are charged with asuitable thermally expansible fluid, preferably a vaporizable fluid, sothat the bellows post 76 is positioned in accordance with the coldestpart of the fluid containing system in a manner which is well understoodby those skilled in the art to which the invention pertains.

The bellows lever 80, which is preferably formed as a sheet metalstamping having a central Web portion 80a and spaced parallel bearingportions 8%, is pivoted at one end between the frame side walls 41a and41b by a pivot pin 81 extending through aligned openings in the bearingportions 80b. The bellows lever 80 has a tab 800 which is bent to form aknife edge engagement with the bellows post 76, and is biased in acounterclockwise direction as viewed in the drawings into followingengagement with the bellows post by an extension spring 83. The spring83, best illustrated in FIG. 6, has a hooked end 83a engaged in openingsin the web portion 80a in the bellows lever 80. The terminalconvolutions of the other end 831) of the spring 83 have engaged thereina nut 85 which threadedly receives an adjusting screw 86 extendingthrough an opening in the top wall 41c of the control frame. The head ofthe screw 86 is provided with a suitable screw driver slot 87 forrotating the screw 86 to adjust the tension of the spring 83 and theloading of bellows 74. A block 90 of insulating material is mounted on ascrew 91 which is threadedly received in an opening in the web portion80a of the bellows lever 80, and the insulating block 90 is engageablewith the switch actuating arm 55.

Decreases in temperature at the bulb 36 below a given temperature, willresult in an appreciable contraction of the bellows 74 and rotation ofthe bellows lever 80 and insulator block 90 in a counterclockwisedirection about the pivot pin 81 under the influence of the spring 83.Such movement tends to withdraw the block 90 from the actuator arm 55 asshown in FIG. 4. Conversely, increasing the temperature at the bulb 36will effect an expansion of the bellows 74 and rotation of the bellowslever 80 and insulator block 91) in a clockwise direction toward theactuator arm 55 as shown in FIG. 5.

The adjustment of the screw 87 and spring 83 is such that when the bulb36 is cooled to approximately 32 F., the bellows 74 will contract andthe bellows arm 80 and insulator block 90 will be moved sufiiciently ina counterclockwise direction to permit the switch actuator arm 55 toeffect toggling of the movable contact 50 against the stationary contact49 to complete a circuit between terminals 45 and 46 for initiating adeice cycle, provided a timed event occurs as described hereinafter.During the deice cycle, the coil 19a is heated to free it of ice and, asthe temperature of the coil 19a and the bulb 36 increases, the bellowsarm 80 and insulator block 90 move in a clockwise direction and towardactuation of the switch 42 to an open position.

In order to require a temperature appreciably above the normal operatingtemperature of the outdoor coil 19a to be attained before the switch 42is actuated to an open position to terminate the deice cycle, there isprovided an additional bellows loading means comprising a secondary loadlever 95. The load lever 95 is conveniently formed as a sheet metalstamping including a central web portion 95a having an opening 95 (FIG.5) through which a portion of the bellows and the block 90 and screw 91extend, and spaced parallel side portions 9512 having at one end alignedopenings receiving the pivot pin 81. The free end 800! of the bellowslever 80 overlies the web portion 95a near the movable end of lever 95which is provided with a tab 950. The tab 950 is engaged by the hookedend 97a of a secondary load spring 97 which is connected by an adjustingscrew 99 and nut 99a to a cam follower lever 98. The lever 98 comprisestabs 98a extending through a slot 417 in the side wall 41b to form apivotal connection therewith, and a projection 9821 at the other end ofthe lever which rides on the peripheral cam surface of a cam 1110. Thecorners of the lever 98 engaging wall 41b are preferably provided withbearing points 980 to minimize friction, and one of the tabs 98a isprovided with a bent over end 98d for retaining the tabs in the slot 41The cam 100 is secured at the inner end of an adjusting shaft 101 whichis rotatably journaled in the side wall 41a of the frame and is providedwith a screw driver slot 10111 for positioning of the shaft and cam. Itwill be recognized that rotation of the cam 100 in a clockwisedirection, as viewed in FIGS. 2 and 4 of the drawings, will act on thecam follower lever 98 to extend the spring 97 and increase theresistance of lever 95 to rotation thereof in a clockwise directionabout the pivot pin 81. The lever 95 is limited in its rotation in acounterclockwise direction about the pivot pin 81 by a stop 102 which isstruck inwardly from the side wall 411;. The end portion 80d of bellowslever 80 is engageable with the web portion 95b of the load lever 95 formoving the latter away from the stop 102 as the temperature of theoutdoor coil 19a is increased above normal operating temperatures duringthe deice cycle. The increased load thereby imposed upon the bellows 74by the load lever 95 and its spring 97 results in a relatively hightemperature being required at the coil 19a to terminate the deice cycle,whereby it is assured that all of the ice is removed. This terminationtemperature may be selectively determined by rotation of the cam 100 toadjust the tension of spring 97 as described above.

In order to permit the initiation of a deice cycle only when both apredetermined low temperature at bulb 36 and a predetermined time occursimultaneously, the device 26 is provided with a timer motor driven camwhich controls the position of a spring biased blocking lever 111 whichis interposed between the cam 110 and an insulating sleeve 112 on anupturned arm portion 55b of the switch actuating lever 55. The blockinglever 111 is conveniently formed from a strip of sheet metal and has aneye 111a formed at one end which receives a pivot pin 113 by which thelever 111 is pivotally mounted between the side Walls 41a and 41b of thecontrol frame. The lever 111 is provided at the other end with a camfollower portion 11112 which rides the peripheral edge or cam surface ofthe cam 110. The lever 111 is biased in a clockwise direction about thepin 113 into following engagement with the cam 110 by a leaf spring 114,one end of which is secured to lever 111 as by a rivet 113a, and theother end of which is engaged in an opening 115 in the control framewall 41s. A screw 116 extends through an opening in lever 111 and isthreadedly engaged in an aligned opening formed in the leaf spring 114.The screw 116 is engageable with the insulating sleeve 112 on actuatorarm 55 and is adjustable to calibrate the relationship between blockinglever 111 and the actuator arm.

The cam 110 is rotated in a clockwise direction, as viewed in thedrawings, by a suitable timer motor such as a synchronous electric motor120 mounted on the side wall 41b of the control frame. Referring toFIGS. 9 and 10, the cam 110 is carried by a stepped shaft 121 having areduced end portion 122 journaled in the side wall 4112, the cam beingsecured against a shoulder 123 by staking of a shoulder 124. A spur gear126 is secured to the shaft 121 between a shoulder 127 thereof and awasher 128, the latter being held in clamping engagement with the gear126 by staking of a shoulder 129 of the shaft. The gear 126 is inmeshing engagement with a drive pinion 131 of the motor 121 which servesto rotate the shaft 121 and the cam 110 at a suitable speed such as onerevolution per hour.

Assuming the cam 110 to be in the position illustrated in FIG. 4 withthe cam follower portion 11111 of lever 111 riding on the high camsurf-ace 117a, the lever 111 is in a position preventing movement of theswitch actuator arm 55 in a clockwise direction to initiate a deicecycle even though an icing temperature is present at bulb 36 and thebellows 74 has contracted to separate the insulator block 91]? from theactuator arm sufficiently to permit actuation of the switch to a closedposition.

As the cam rotates, the cam follower portion 11112 of lever 111 ridesonto surface 118a and drops into recess 119a, thereby permitting theactuator arm 55 to rotate to its FIG. 5 position, causing the cont-act50 to engage contact 49 and initiate a deice cycle. Continued rotationof the cam 110 returns the cam follower portion to surface 1180, but theaccompanying rotation of actuator arm 55 in the counterclockwisedirection is insuflicient to overcome the above mentioned differentialbetween operative positions thereof, and the deice cycle continues.

As the temperature of coil 19a and bulb 36 rises, the lever 80 isrotated in a clockwise direction and the end portion 8M thereof picks upthe secondary load lever 95 as shown in FIG. 5. During this movement theblock 90 engages and rotates the arm 55 in a counterclockwise directionuntil the maximum desired temperature of coil 19a is reached and, asshown in FIG. 6, the switch 42 is actuated to an open conditionterminating the deice cycle. Thereafter, the evaporator returns to itsnormal operating temperature, in which condition the bellows contractsan amount less than that required to withdraw block 90 from arm 55 to aposition permitting actuation of the switch even if one of the camrecesses 119a, 11% passes under the cam follower portion 111b.

Of course, if an icing temperature occurs at the coil 1% and the bellows74 has contracted further to bring lever 80 and block 90 to their FIG. 4positions, then registration of either of the recesses 11%, or 11% withthe cam follower portion 111b will result in initiation of a defrostcycle. It will be recognized that the control device 26 provides for theinitiation of a deice cycle when predetermined icing temperature andtime conditions exist simultaneously, and that the deice cycle isterminated in response to a predetermined high temperature condition.

The control device 26 of this invention provides for positivetermination of the deice cycle in the event of a failure of thetemperature responsive means, for example if leakage of the fluidtherefrom permits the bellows 74 to collapse. Thus, if the deice cyclehas not been terminated by the temperature responsive means within apredetermined time interval, the lever 111 is rotated in acounterclockwise direction by the cam 110 as the cam follower portion111b rides from the relatively low surface 118a or 1181; to a highersurface 117]) or 117a, respectively. Thereafter, the initiation andtermination of the deice cycle will be effected solely on a time basis.

Under some operating conditions, such as prevailing high humidity, it isdesirable to provide more frequent deicing cycles than when operatingunder drier conditions. Accordingly, the control device 26 contemplatesthe inclusion of means for alternatively masking or unmasking one of therecesses (11912) in the periphery of the cam 110, whereby the device 26may be selectively conditioned to provide either one or two deicingcycles for each revolution of the cam. To this end, there is provided amask 135, FIGS. 6, 9, and 10, having a ring portion 135a rotatablymounted on the shaft 121 between a shoulder 136 thereof and adish-shaped spring washer 137, the peripheral edge of which bearsagainst the gear 126. The spring washer 137 serves as a clutchfrictionally holding the mask 135 for rotation with the earn 110, butpermitting the mask to be forcibly rotated with respect to the cam fromthe full line position of FIG. to the dotted line position 135' whereinthe end of the mask registers with recess 11% to prevent cam followerportion 111b of lever 111 from dropping into that recess upon rotationof the cam 110.

The rotation of the mask 135 with respect to the cam 110 is convenientlyeffected through the agency of a sleeve 140 surrounding the shaft 121and having a recess 141 receiving a tab 135]; which extends from themask ring 135a through an arcuate opening 142 in the cam 110. The sleeve140 projects through, and is journaled in the frame side wall 41a. Itwill be seen that rotation of the sleeve 140 about the shaft 121 caneffect swinging movement of the mask 135 through an arc of approximately90 as determined by arcuate slot 142 in cam 110 for masking andunmasking recess 11%. The cam 110 and shaft 121 are prevented fromturning during movement of the mask 135 by engagement of the gear 126with pinion 131 which is driven by the motor through reduction gearinghaving such a ratio as to preclude overrunning. The sleeve 140 isconveniently provided with index marks, for example the numerals 1 and 2shown on the sleeve in FIG. 1, which may be aligned with a screw driverslot 121a in shaft 121 to select one or two timed periods, respectively,per revolution of cam 110.

From the foregoing detailed description of my invention, it will beappreciated that there has been provided thereby an improved andparticularly effective deice control which is responsive to both timeand temperature to control deice cycles of a refrgerating system.

Although the invention has been described in considerable detail withreference to a specific deice control embodying the invention, it willbe understood that the invention is not limited thereto, but rather theinvention includes all those modifications, substitutions, adaptationsand uses as are reasonably embraced by the scope of the claims hereof,

Having described our invention, we claim:

1. In a control mechanism for heat pumps and the like, an electric snapswitch mechanism having an actuator arm movable between two switchoperative positions, means continually urging said arm towards a singleone of said positions, a first blocking means movable into and out ofthe path of movement of said arm to block movement toward said oneposition, thermally responsive means to move said blocking means intoand out of said path, a second blocking means movable along said path ofmovement of said arm and adapted to be engaged by said arm and separabletherefrom when said arm is blocked by said first blocking means, andtimer driven cam means for moving said second blocking means in oppositedirections along said path of movement.

2. A control mechanism as defined in claim 1 further characterized bysaid control mechanism including a housing in which said switch, firstand second blocking means and cam operated timer are enclosed, and saidsecond blocking means comprising a leaf spring supported in said housingand engaged by said arm and adapted to be flexed by said cam means tomove said arm towards said second position.

3. A control mechanism as set forth in claim 1 further characterized bysaid actuator arm being L-shaped and having portions arranged atsubstantial right angles to one another, one of said portions beingengageable by said first mentioned blocking means and the other of saidportions normally engaging said second blocking means.

4. In a control mechanism for heat pumps and the like, an electric snapswitch mechanism having an actuator arm movable between two switchoperative positions, means continually urging said arm toward one ofsaid positions, a first blocking means movable into and out of the pathof movement of said arm to block movement toward said one position,thermally responsive means comprising a first lever supporting saidfirst blocking means, an expansible element for moving said lever in adirection to position said first blocking means in said path of movementof said actuating arm by expansion of said element, said first levermoving in the opposite direction in response to contraction of saidelement, a second lever engageable by said first lever during movementthereof to move said blocking means in the path of said arm, springmeans loading said second lever to resist movement thereof by said firstlever, means to limit travel of said second lever in the direction saidfirst lever moves in response to contraction of said element, a secondblocking means movable along said path of movement of said arm andadapted to be engaged by said arm and separable therefrom when said armis blocked by said first blocking means, and timer driven cam means formoving said second blocking means in opposite directions along said pathof movement.

5. In a control mechanism for heat pumps and the like, an electric snapswitch mechanism having an actuator arm movable between two switchoperative positions, means continually urging said arm toward one ofsaid positions, a first blocking means movable into and out of the pathof movement of said arm to block movement toward said one position,thermally responsive means to move said blocking means into and out ofsaid path, a second blocking means movable along said path of movementof said arm and adapted to be engaged by said arm and separabletherefrom when said arm is blocked by said first blocking means, timerdriven cam means for moving said second blocking means in oppositedirections along said path of movement, a housing in which said switch,first and second blocking means and cam operated timer are enclosed,said second blocking means comprising a leaf spring supported in saidhousing and engaged by said arm and adapted to be flexed by said cammeans to move said arm toward said second position, said cam meanscomprising a disc rotatable on an axis 9 10 normal to the direction ofmovement of said actuator 2,674,665 4/1954 Raney et al. ZOO-136.3 armand having a periphery of irregular diameter for con- 2,697,332 12/ 1954Duncan ZOO-136.3 trolling the movement of said leaf spring in oppositedi- 2,711,456 6/1955 Goodhouse ZOO-136.3 rections along said path of moement of said actuator 2,729,718 1/ 1956 Liebermann 200l36.3 arm, andmeans to alter the effective diameter of said cam. 5 FOREIGN PATENTSReferences Cited by the Examiner 229,054 4/1958 Australia.

UNITED STATES PATENTS BERNARD A. GILHEANY, Primary Examiner. 1,420,3486/1922 Swift 236-46 1,430,852 10/1922 Roesch 200-136.3 10 T. D.MACBLAIN, H. A. LEWITTER, L. A. WRIGHT, 1,975,851 10/1934 Kimball 23646Assistant Examiners.

1. IN A CONTROL MECHANISM FOR HEAT PUMPS AND THE LIKE, AN ELECTRIC SNAPSWITCH MECHANISM HAVING AN ACTUATOR ARM MOVABLE BETWEEN TWO SWITCHOPERATIVE POSITIONS, MEANS CONTINUALLY URGING SAID ARM TOWARDS A SINGLEONE OF SAID POSITIONS, A FIRST BLOCKING MEANS MOVABLE INTO AND OUT OFTHE PATH OF MOVEMENT OF SAID ARM TO BLOCK MOVEMENT TOWARD SAID ONEPOSITION, THERMALLY RESPONSIVE MEANS TO MOVE SAID BLOCKING MEANS INTOAND OUT OF SAID PATH, A SECOND BLOCKING MEANS MOVABLE ALONG SAID PATH OFMOVEMENT OF SAID ARM AND ADAPTED TO BE ENGAGED BY SAID ARM AND SEPARABLETHEREFROM WHEN SAID ARM IS BLOCKED BY SAID FIRST BLOCKING MEANS, ANDTIMER DRIVEN CAM MEANS FOR MOVING SAID SECOND BLOCKING MEANS IN OPPOSITEDIRECTIONS ALONG SAID PATH OF MOVEMENT.